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The high-current diffuse column arc in vacuum consists of a bright central column of plasma, with some number of individual cathode spots burning on the remainder of the contact surface. The arc voltage imposed by the main column alters the plasma expansion and current flow of single jets burning alongside the column. Stable existence of the displaced single jets drives the transition into the high-current diffuse mode. The new model assumes that the displaced single jets are confined along the magnetic field, which is a combination of a self-magnetic field and an axial magnetic field. Azimuthal self-magnetic field leads to increase in the effective length of the jet path between two contacts. The longer effective length leads to higher critical voltage below which single jets can stably exist without a source of additional plasma. This produces conditions favorable to single-jet stability. A generalized criterion for single-jet existence is presented.